Method of producing images on rigid surfaces



Patented May 5, 1953 METHOD OF PRODUCING IMAGES ON RIGID SURFACES HaroldE. Copley, Columbus, Ohio, assignor, by mesne assignments, to TheBattelle Development Corporation, Columbus, Ohio, a corporation ofDelaware No Drawing. Application October 2, 1948,

' .Serial No. 52,591

6 Claims. 1

This invention relates to a method of producing an image on a printingelement such as an electroprinting or lithographic plate or other rigidsurface from a powder image on an electrophotographic plate, withparticular reference to making a metal printing plate or cylinder forproducing multiple copies of an image which has been formed on theelectrophotographic plates by electrically-charging a photoconductinginsulating layer on the conductive backing of the plate and exposing thecharged layer to produce an electrostatic image to which electroscopicpowder is applied to form a powder image, and it has for its purpose toafford a practical, simple and expedient way of successfully producing aprinting element which has pronounced advantages over methods heretoforeproposed and of successfully transferring such a powder image on theconductive backing of the plate to any hard, nonyielding or rigidsurface.

With the previously known methods of preparing printing plates orcylinders by electrophotographic methods according to which a powderimage is transferred directly from an electrophotographic plate to aprinting element and fused thereto, it has not been possible to producesatisfactory metal printing plates owing to irregularities in thecontacting surfaces of the metal printing plate and theelectrophotographic plate, because of which as well as other factors,printing plates made in this fashion have failed in many instances tofunction, and it is a purpose of this invention to afford a method oftransferring a powder image from one metal plate to another metal orother rigid or non-yielding surface so as to enable the production ofuniformly satisfactory metal printing elements, either metalelectroprinting plates and cylinders for electrically reproducingmultiple copies or metal lithographic plates for multiple reproductionof copies.

Another objection to the rigid surface to rigid surface method ofproducing printing plates using an electroscopic powder has been that inorder for the printing element to carry a reversal of the image, whichis required for printing processes other than offset-printing, or wherethe printing element engages and prints directly on the paper, theremust be a mirror projection of the image on to the electrophotographicplate or typed copy must have carbon reversal on the back, which gives aweaker image than is desired or an image wherein the lines are frayedand not clear cut and it is a further purpose of the present inventionto afford a method by which the powder image, which, is amirror reversalof the subject,

is duplicated as a clear out strong image on the printing plate or othersupport because the subject can be projected directly on to theelectrophotographic plate.

Still a further purpose of the invention is to overcome defects in theprinting element, resulting from irregularities in theelectrophotographic or printing plates, by transferring the powder imagefirst from the electrophotographic plate to a paper or flexible transfersheet in contact therewith by electrically charging the transfer sheetand then transferring the powder image from the paper transfer sheet tothe printing element While in contacttherewith by electrically chargingthe transfer sheet with a charge of opposite polarity to the chargewhich effects transfer from the electrophotographic plate to thetransfer sheet.

The invention is carried out in connection with a powder image formed onan electrophotographic plate in the manner disclosed in patentapplication of Lewis E. Walkup and Edward N. Wise, filed May 1, 1948,Serial No. 24,674, according to which a photoconductive insulating layeris subjected to an electrostatic charge and then exposed to produce anelectrostatic image on the layer after which suitable electros-copicpowder is dusted over the electrostatic image to produce the powderimage, and the present invention has to do with transferring such powderimage to a metal printing plate, cylinder, lithographic plate forcontinuously producing multiple copies, or other rigid or non-yieldingsupport.

It has been found that satisfactory results cannot be obtained bytransferring a powder image from a rigid plate directly from theelectrophotographic plate to a metal printing plate, metal lithographicplate, or other rigid or non-yielding support, and in order to overcomethe existing objections and to-obtain a satisfactory printing elementwith an accurate clear lined powder image correctly placed thereon, thepowder image is first transferred from the electrophotographic plate toa paper or other flexible transfer sheet, while positioned in contactwith the powder image by applying an electrostatic charge to theflexible transfer sheet by means of suitable corona discharge needles orother electrical charging instrumentalities, resulting in creating anelectric fleld around the powder image and between the powder image andthe transfer sheet, causing the latter to be attracted electricallyagainst the powder image and electrophotographic plate, the transfersheet being held by electrical attraction firmly against the powderimage while the powder particles are attracted toward and held by thetransfer sheet, all of which is in accordance with the proceduredisclosed in pending application of Roland M. Schaffert, Serial No.21,737, filed April 17, 1948, now abandoned.

During the operation just described, the paper or flexible sheet adheresclosely to the electrophotographic plate and conforms to anyirregularities that may exist in the plate so that the powder image isaccurately transferred to the flexible transfer sheet in the exactrelationship which it occupies on the electrophotographic plate,following which the powder image, which is now held on the flexibletransfer sheet by electrostatic attraction, is transferred to theprinting plate, printing cylinder, or lithographic plate in the mannernow to be described, and permanently affixed thereto.

To accomplish this, the transfer sheet is then positioned with theunfused and electrically held image face down, in contact with the metalprinta ing Plate or other printing element to which thepowder image isto be transferred, the surface of the printing element having first beenthoroughly cleaned, and an electrostatic or other electrical charge isthereupon sprayed or otherwise imposed on or applied to the flexibletransfer sheet by suitable corona discharge needles or other electricalcharging mechanism, similarly to the mechanism disclosed in theaforesaid copending application Serial No. 21,737.

In order to effect movement of the powder particles forming the imageaway from the flexible transfer sheet and into intimate engagement withthe metal or other printing element, the electric charge imposed on theflexible transfer sheet has a polarity opposite to that of the chargeused in transferring the powder image from the electrophotographic plateto the transfer sheet, as a consequence of which the powder image isrepelled from the flexible transfer sheet and attracted to the surfaceof the printing element to which it adheres. After the powder image hasbeen entirely transferred from the flexible sheet to the metal printingplate or other printing element, the transfer sheet is removed and thepowder image thereupon fused or otherwise permanently afiixed to theprinting element, which is then ready for making multiple copies bycharging the permanent image electrostatically, dusting the same withelectroscopic powder, and transferring the resultant powder image to apaper or other support, or by the usual lithographic printing process.

In cases where a lithographic plate is produced, the same procedure asdescribed above is followed except that the electroscopic powderemployed is of such a character as to be properly wetted by lithographicink in addition to responding to the electrical forces set up intransferring the powder from the electrophotographic plate to theflexible transfer sheet and from the fiexible transfer sheet to thelithographic plate. To effect this, any of the resinous electroscopicpowders such as disclosed in the aforesaid copen'ding application serialNo. 24,674 can be suc-- cessfully used, and most of the knownelectroscopic powders employed in electro'photograp'hy aresatisfactoryfor lithographic purposes, after the powder image is permanently afflxedto the lithographic plate.

The procedure herein described has the advantage that the flexibletransfer sheet, when in contact with the electrophotographic plate andsubsequently with the printing plate or printing element, readilyconforms to irregularities or imperfections in the respective plates,and thus the powder image on the electrophotographic plate is accuratelytransferred and reproduced on the printing element bringing about aresult that cannot be had where transfer is made directly from anelectrophotographic plate to a metal printing plate. A further advantagelies in the fact that the image on the printing plate is a reversal ofthe original subject being copied, making it unnecessary to employ amirror in photographing the copy or to type cop with a carbon at theback for contact work. Where transfer of a powder image is made directlyfrom an electrophotographic plate to a printing element, provision mustbe made to provide the printing element with a reversal of the originalsubject, and. this is obviated with the present invention.

In addition to making printing plates, the invention may be utilized forproducing templates, name plates, decorating wood, metal, plastic, glassor porcelain surfaces, or other rigid, non-yielding surfaces to which animage or decoration is to be transferred, and photoengraving plates canalso be made according to the invention by etching the metal plate afterfinal transfer of the image thereon.

While the invention has been described with reference to a more or lessspecific procedure, it is not limited to the detailed steps hereindisclosed, and this application is intended to cover such departures ormodified procedures as may come within the purposes of the improvementand the scope of the following claims.

I claim:

1. The method which comprises transferring a powder image from anelectrophotographic plate to a flexible transfer sheet by means of anelectric charge applied by corona discharge to the transfer sheet whilethe latter is in contact with the plate, then transferring the powderimage from said flexible transfer sheet to the rigid surface of aprinting element by means of an electric charge applied by coronadischarge to the transfer sheet while the latter is in contact with theprinting element, and fixing the powder image on said printing element.

2. The method which comprises transferring a powder image from anelectrophotographic plate to a flexible transfersheet by means of anelectric charge applied by corona discharge to the transfer sheetwhilethe latter is 'lncontact with the plate, then transferring the powderimage from said flexible transfer sheet to a rigid surface of aprinting'element by means of an electric charge applied by coronadischarge to the transfer sheet while the latter is in contact with theprinting element, said charge having a polarity opposite to that of thefirstmentioned charge, and fixing the powder image on said printingelement.

3. The method of transferring an electroscopic powder image from aninitial supporting surface to a final supporting surface which comprisesplacing a transfer sheet of flexible insulating material against saidinitial surface carrying said powder image and applying an electrostaticcharge to the back of said transfer sheet, said charge being opposite inpolarity to the predominant charge on said powder, thereby to effecttransfer of at least part of said powder tosaid transfer sheet, removingsaid transfer sheet with its adhering powder image from said initialsurface, placing the image-bearing face thereof against said finalsurface, then -.applying a second electrostatic charge to the back ofsaid transfer sheet, said second charge being opposite in polarity tothe first-mentioned charge applied to said transfer sheet, thereby toeffect transfer of at least part of said previously transferred powderimage to said final surface, and then removing said transfer sheet fromsaid final surface.

4. The method as claimed in claim 3 in which said initial surface is thephotoconductive insulating coating of an electrophotographic plate.

5. The method as claimed in claim 3 in which said initial and finalsurfaces are rigid.

6. The method as claimed in claim 3 in which said initial surface is thephotoconductive in- 15 2383362 References Cited in the file of thispatent UNITED STATES PATENTS Number Name Date 420,765 Brings Feb. 4,1890 526,557 Brookman Sept. 25, 1894 2,297,691 Carlson Oct. 6, 19422,376,922 King May 29, 1945 2,408,144 Huebner Sept. 24, 1946 HuebnerOct. 4, 1949

1. THE METHOD WHICH COMPRISES TRANSFERRING A POWDER IMAGE FORM ANELECTROPHOTOGRAPHIC PLATE TO A FLEXIBLE TRANSFER SHEET BY MEANS OF ANELECTRIC CHARGE APPLIED BY CORONA DISCHARGE TO THE TRANSFER SHEET WHILETHE LATTER IS IN CONTACT WITH THE PLATE, THEN TRANSFERRING THE POWDERIMAGE FROM SAID FLEXIBLE TRANSFER SHEET TO THE RIGID SURFACE OF APRINTING ELEMENT BY MEANS OF AN ELECTRIC CHARGE APPLIED BY CORONADISCHARGE TO THE TRANSFER SHEET WHILE THE LATTER IS IN CONTACT WITH THEPRINTING ELEMENT, AND FIXING THE POWDER IMAGE ON SAID PRINTING ELEMENT.